The present invention relates to an adjusting unit for actuating a device for variable control of valves of an internal combustion engine for load control of the engine via the inlet stroke function of the valves.
A device for variable control of valves of an internal combustion engine can be embodied in various ways in accordance with the prior art. One possible embodiment of such a device for instance has two camshafts, which are rotatable about their longitudinal axes and which act on the valves. The first camshaft determines the open function and the second camshaft determines the close function of the valves. By a relative rotation of the camshafts to one another, the stroke and opening duration of the valves can be varied Such devices are known for instance from the article entitled "Kurbeltrieb fur variable Verdichtung" [Crank Drive for Variable Compression], MTZ Motortechnische Zeitschrift 58 (1977), 11, pages 706-711.
The rotation of the two camshafts relative to one another is effected for instance by means of a multi-wheel coupling gear, of the kind known from German Patent Disclosure DE 42 44 550 A1. In this reference, a so-called variable valve drive is disclosed, in which the rotation of the two camshafts relative to one another is effected by a four-wheeled coupling gear. The wheels of the coupling gear mesh in pairs with one another. The first wheel of the coupling gear, embodied as the drive wheel, is connected to the first camshaft in a manner fixed against relative rotation. The longitudinal axis of the first camshaft coincides with the pivot axis of the drive wheel. The fourth wheel, embodied as a driven wheel, is connected to the second camshaft in a manner fixed against relative rotation. The longitudinal axis of the second camshaft coincides with the pivot axis of the driven wheel. The drive wheel and the driven wheel of the coupling gear do not mesh directly with one another directly but instead mesh via the two wheels of the coupling gear that are embodied as intermediate wheels. In this way, a chain of wheels meshing with one another, extending from the drive wheel through the two intermediate wheels to the driven wheel, is obtained.
The four wheels of the coupling gear are connected to one another via a coupling linkage, which comprises three coupling rods pivotably connected to one another. One end of the first coupling rod is pivotably connected to the pivot axis of the drive wheel, and one end of the third coupling rod is pivotably connected to the pivot axis of the driven wheel. Between the first and the third coupling rods, the second coupling rod is disposed in such a way that the pivot points between the coupling rods are located on the pivot axes of the intermediate wheels.
The drive wheel and the driven wheel mesh with one another via the two intermediate wheels in such a way that a rotary motion of the drive wheel is converted via the intermediate wheels into a contrary rotary motion of the driven wheel. The pivot axes of the two camshafts are disposed so as to be stationary. The first coupling rod, which connects the drive wheel to the first intermediate wheel, is embodied as an actuating lever and lengthened past the pivot axis of the first intermediate wheel. An adjusting unit is pivotably connected to the actuating lever and by it the actuating lever can be pivoted about the pivot axis of the drive wheel. As a result, the coupling linkage is pivoted in a pivoting plane such that the intersection points of the pivot axes of the intermediate wheels with the pivoting plane are located on unambiguously defined paths. When the coupling linkage is pivoted, the driven wheel and thus the second camshaft are rotated in a rotational motion counter to the first camshaft. The rotational motion is the product of a superposition of the pivoting motion of the coupling linkage and the rolling motion of the wheels on one another.
A number of demands are made of the adjusting unit. To achieve unthrottled load control over the entire operating range of modern internal combustion engines, the inlet stroke function of the valves must be adjustable over a wide range. To enable covering such wide adjustment ranges, the adjusting unit must have a relatively long translational adjustment path. In addition, given the demands made of the engine in terms of dynamic operation, it must be possible to traverse this adjustment path within the briefest possible time, that is, within only a few tenths of a second. Finally, the adjusting unit must also be capable of maintaining each set point with high precision, in the face of the pulsating forces of reaction from the valve drive.
From the prior art, it is known to embody the adjusting unit as a hydraulic adjusting unit with a cylinder and a piston. Adjusting units embodied in this way are used to actuate a device for variable control of valves of an internal combustion engine, of the kind known from DE 42 44 550 A1.
Such hydraulic adjusting units are relatively complicated and labor-intensive both to manufacture and to operate and maintain. The result is relatively high costs for such an adjusting unit.